This invention relates to an apparatus for and a method of transferring conductive balls onto a workpiece (e.g. a board or an electronic device such as a ball grid array).
Recently, there has been proposed a solder ball-transferring apparatus for transferring a plurality of solder balls at a time. FIG. 5 shows the operation of such a conventional solder ball-transferring apparatus.
In FIG. 5, reference numeral 1 denotes a ball reservoir for holding a number of solder balls 2 therein, and this ball reservoir 1 has an open top through which a suction head 3 is movable into and out of the ball reservoir 1. The suction head 3 has a plurality of suction holes 3a formed in its lower surface in a matrix pattern, so that the suction head 3 can pick up a plurality of solder balls 2 at a time by suction. Here, the suction head 3 is designed such that each suction hole 3a can hold one solder ball 2 by suction.
Actually, however, an extra solder ball b other than one solder ball a is often drawn to be held by the suction hole 3a under suction, or extra solder balls c stick to the lower surface of the suction head 3, as shown in FIG. 5. As a result, these extra solder balls b and c are transferred onto a workpiece.
It is desired to increase the suction pressure so that the solder balls 2 will not drop during the movement of the suction head 3. However, if the suction pressure is increased in the conventional solder ball-transferring apparatus, the solder balls 2 are excessively held by the suction holes 3a under suction, and even when the suction condition is released so as to place the solder balls 2 onto the workpiece, the solder balls 2 often failed to drop from the suction head 3, so that the solder balls 2 could not be properly transferred onto the workpiece. Thus, the conventional solder ball-transferring apparatus has a problem that the pick-up of the solder balls from the solder ball reservoir, as well as the transfer of the solder balls onto the workpiece, can not be carried out in a highly reliable manner.